1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, a driving method therefor, and a display system.
2. Background of the Invention
A conventional liquid crystal display apparatus is, for example, disclosed in the Japanese Unexamined Patent Publication No. 6-222741. FIG. 2 is a circuit diagram of a data driver in the liquid crystal display apparatus. Data driver systems for writing an image signal into a liquid crystal display apparatus generally includes an analog system and a digital system. Since the analog system consumes a large power in the circuit, it is not suited to a display for a portable computer. In contrast, the digital system consumes a small power, but it requires that an output voltage be supplied from the outside and the number of external power sources becomes large. There is a system in which a D/A converter is built and the number of external power sources is made minimum. Since the output voltage of a D/A converter is linear in general and its linearity differs from the g characteristic of liquid crystal, this system is not suited to gray-scale display. Therefore, the difference between input voltages is interpolated and output to conduct g correction to some extent while the number of external power sources is reduced.
In the circuit shown in FIG. 2, for example, nine levels of voltages are externally supplied and a total of 64-level output voltages can be output. V1, V2, . . . and V9 are externally given nine power source voltages. The three high-order bits 21 of an image signal are converted to eight-value data in a decoder 23. Power selection circuits 24 and 25 select two adjacent power sources from these nine power source voltages. The three low-order bits 22 of the image signal are converted into eight-value data. A resistor-division-type D/A converter 26 selects and outputs one voltage from equally divided eight voltages between the two selected voltage levels. In this system, when the nine power source voltages input externally are made optimum according to the g characteristic of the liquid crystal, g correction can be achieved to some extent.
A conventional TFT circuit, however, has the following drawback. An interpolated and output voltage differs from the voltage to be ideally displayed. This point will be described below by referring to the drawings. FIG. 3 is chart indicating the relationship between the applied voltage and the transmission ratio of the liquid crystal display apparatus. An actual liquid crystal display apparatus has a transmission-factor dependency indicated by a dotted curve 31. Since the data driver circuit shown in FIG. 2 uses the nine input power source voltages, V1, V2, . . . , and V9, to interpolate the output voltages, a transmission ratio dependency shown by a broken line 32 is assumed. FIG. 4 is a partially enlarged view of FIG. 3. When the difference between two input voltages V1 and V2 is equally divided into eight sections and the output voltages, Va, Vb, Vc, Vd, Ve, Vf, and Vg, are applied to the liquid crystal display apparatus, the corresponding gray scale is displayed with Ta, Tb, Tc, Td, Te, Tf, and Tg, and shows white compression.